Seatbelt retractors having a two-spring comfort function are known in principle from the publications DE 43 15 886 A1, DE 196 11 748 C2, DE 199 52 371 C1, DE 101 62 374 C1, and DE 103 38 865 A1 and serve to wind up the seatbelt with a higher spring force when removing than when wearing, by which an increased feeling of comfort is conveyed to the occupant by the reduced retraction force of the seatbelt when worn. In those solutions the different spring force acting on the seatbelt is realized by two retraction springs having a different spring force. The stronger retraction spring, also known as the roll-up spring, is tensioned by its outer end in a fixed manner with respect to the housing attached by its inner end to a ratchet wheel of the webbing spool. The weaker retraction spring, also referred to as the comfort spring, is held by its outer end on the ratchet wheel and by its inner end on a take-up sleeve connected to the belt shaft for conjoint rotation therewith. The retraction springs are thus connected in series. In principle, in this case the roll-up spring acts via the ratchet wheel, and the close-wound comfort spring acts on the belt shaft. The comfort spring only acts if the ratchet wheel is fixed with respect to the housing, so that the ratchet wheel in this case acts as a support for the comfort spring, which support is fixed with respect to the housing. In this case the roll-up spring is deactivated by the fixing of the ratchet wheel. Thus either the comfort spring or the roll-up spring act depending on whether the ratchet wheel is fixed. The ratchet wheel is fixed, depending on the extension length of the seatbelt, using a locking pawl whose movement is controlled by a mechanical counting mechanism, disposed on the belt shaft, or an actuator.
It is a disadvantage of this solution that during switching, i.e., during releasing of the ratchet wheel, the comfort spring is abruptly fully recoiled, wherein in particular with abrupt braking in the locked position relatively high forces act on the comfort spring and on the ratchet wheel. To reduce forces acting on the comfort spring during switching, it is proposed, e.g., in DE 196 11 748 C2, to provide an additional spring element between the ratchet wheel and the end of the comfort spring, which end is held on the ratchet wheel.
Against this background, the object of the invention is to provide a seatbelt retractor having an improved two-spring comfort function.
To achieve this object, according to the invention a seatbelt retractor having the features described herein is proposed.
In accordance with the basic principles of the invention it is proposed that the retraction springs are disposed in parallel between the belt shaft and the housing, and at least one of the retraction springs is connectable by one end to the belt shaft or the housing via a switch device switched depending on the extension length of the seatbelt. Using the proposed solution neither of the two retraction springs any longer needs to be fully recoiled during the switching process, since each of the retraction springs acts between the belt shaft and the housing independently of the respective other retraction spring. As a result, the problems known in the prior art do not arise, and furthermore the functioning of the retraction springs is not dependent on the functioning of the respective other retraction spring. In addition, one of the retraction springs can act practically permanently between the belt shaft and the housing, so that it provides a type of basic retraction force, while increasing of the retraction force to retract the seatbelt into the parked position is effected by connecting of the respective other retraction spring. Since the retraction springs act in parallel, the spring forces are added together, and neither of the retraction springs needs to be designed to apply the entire retraction force that is needed for winding up the seatbelt into the parked position. Here the spring characteristic curve can be matched to a specified characteristic curve by providing a number of retraction springs and optional connection, by simple constructive means via the switching device, of the ends of the retraction springs either to the belt shaft or to the housing.
It is further proposed that one of the ends of the retraction springs is held on a coupling part, on which a movable locking part is provided, which connects the coupling part to the belt shaft in one position, and that the movement of the locking part is controllable by the switching device. The coupling part and the locking part serve to connect the end of the retraction spring to the belt shaft or the housing, wherein the coupling part serves to hold the end of the retraction spring, and the locking part serves to produce the connection of the coupling part to the belt shaft or the housing.
It is further proposed that a take-up sleeve non-rotatably connected to the belt shaft is provided, on which take-up sleeve a second end of the retraction spring is non-rotatably held, and to which the locking part, in the position connecting the coupling part to the belt shaft, engages in a locking manner counter to the retraction direction of the safety belt. The take-up sleeve is thus used for connecting the two ends of the retraction springs to the belt shaft.
It is further proposed that the switching device includes a linearly displaceable switching part for controlling the movement of the locking part, and that the movement of the switching part by the switching device is controlled as a function of the extension length of the seatbelt.
In this case it is further proposed that the switching part is non-rotatably fixed to the housing and has a cam contour on which the locking part abuts. The locking part is disposed on the coupling part, which, in the position connecting the coupling disc to the belt shaft, executes the rotary movement of the belt shaft together with the coupling disc. The switching part, however, is non-rotatably secured to the housing, so that the locking part executes a relative rotary movement with respect to the switching part. In this case a movement of the locking part can very simply be forced by the abutment of the locking part on the cam contour, which movement is specified by the shape of the cam contour. Here the switching part having the cam contour can be brought into various positions by the linear switching movement. At the start of the extension movement the switching part can be located, e.g., in a position wherein the coupling part having the locking part can rotate without the locking part being forced to move, i.e., the locking part does not abut with the cam contour, or the cam contour has a course such that the locking part, despite abutting on the cam contour, is not forced to move. Due to the switching of the switching part the cam contour is linearly displaced into a second position wherein the locking part is forced into a pivoting movement, for example, due to which the connection between the coupling part and belt shaft is released. The reverse movement of the locking part is then effected by a return movement of the switching part into the original position and rotation of the belt shaft in the other direction.
It is further proposed that two projections are provided on the locking part, which projections each abut with the cam contour depending on the position of the switching part, and when abutting the cam contour, by execution of a relative movement of the locking part with respect to the switching part, control the movement of the locking part. In the case of the movement of the locking part out of the position connecting the coupling part to the belt shaft into the release position, the relative movement of the locking part is forced by the rotary movement of the belt shaft with respect to the switching part, since in this phase the locking part is connected to the belt shaft. In this case after the release of the locking part, the relative movement of the locking part for forcing the reverse movement is effected by the spring-force-supported movement of the coupling part with respect to the switching part.
Here the movement of the locking part is preferably controlled such that for connecting the coupling part and/or for releasing the connection of the coupling part to the belt shaft it is moved to a ready position, from which, supported by the spring force of the retraction spring connected to the coupling part, it can be moved into a final position that connects or does not connect the coupling part to the belt shaft. The ready position can thus be regarded as a type of prepositioning, from which the locking part can rotate into a final position only by the spring-force-supported further rotating movement. Such a ready position is useful in particular for releasing the connection between the coupling part and the belt shaft, since the movement direction of the locking part during this movement sequence must be reversed in a final phase to a pure rear engagement behind of the locking part.
It is further proposed that the retraction springs are formed by two coil springs disposed parallel to each other, and the coupling part by a coupling disc disposed between the coil springs. Using the proposed solution a constructively simpler design results, and the coupling part furthermore serves, due to its disc shape, as a lateral abutment surface for at least one of the retraction springs.
In particular the locking part can be formed by a pivotable locking pawl. Here the locking pawl is preferably supported on the coupling part.
A very cost-effective, purely mechanical solution of the switching device can thereby be realized by a switching device in the form of a mechanical counting mechanism driven by the belt shaft. Here the counting mechanism serves as a device for detecting an extension length of the seatbelt, which extension length is specified by the design of the counting mechanism. Here conceivable and proven embodiments of the counting mechanism are wobble transmissions or reduction gearboxes including a plurality of mutually engaging gear wheels and corresponding switching cams, or even a control disc driven via a reduction gearbox.
A particularly constructively simple embodiment of the counting mechanism can be realized in that a counting mechanism having a wobble disc driven by the belt shaft via an eccentric, which wobble disc traverses the belt shaft with a gearing in a housing-fast gearing, and in that two projections are provided, both on the wobble disc and on the switching part, which projections in one position each abut with one another in pairs, and thereby force the linear switching movement of the switching part. In this case the counting mechanism is realized solely by two additional parts, namely the eccentric and the wobble disc, which are cost-effectively manufacturable in high volume as injection-molded parts.
Alternatively, the switching device can also include an electrically operable actuator, which allows particularly precise control of the switching movement. Here either the movement of the locking part can be directly controlled, or the movement of the switching part can be controlled.
Furthermore, preferably identical retraction springs can be used, whereby the manufacturing costs can be reduced further.
It is further proposed that the switching device is disposed such that it intersects at least one plane spanned by the retraction springs, wherein the switching device is particularly preferably disposed inside the innermost winding of one of the retraction springs. Using the proposed solutions the necessary installation space requirement can be reduced and a particularly compact seatbelt retractor can be provided. Furthermore, the switching device is thereby already disposed spatially very close to one of the ends of the retraction spring, so that the switching movement can be transmitted very simply to this end.